This invention relates in general to bicycle variable speed transmission systems, and more particularly, to a fully automatic torque converter transmission having a low speed high torque positive drive state transformable into an infinitely variable higher speed shift mechanism.
There have been efforts in the past to provide variable drive bicycle transmissions in place of stepped speed bicycle transmissions such as the traditional "Ten-Speed Derailleur". Such efforts are typified by the "Variable Drive Bicycle Transmission" U.S. Pat. No. 3,972,244 of which I am a co-inventor, that varies the mechanical advantage via use of a "V" belt fixed pitch sheave rotatably mounted on the bicycle frame and a variable pitch sheave interconnected by a "V" belt. The rotation of the variable pitch sheave by action of the pedal sprocket in this structure causes the movement of the variable pitch sheave relative to the fixed pitch sheave to vary the mechanical advantage therebetween. Use of a second "V" belt sheave adds belt to sheave friction losses incurred thereby and there is no positive drive in any drive speed state of this transmission. Applicant's new transmission offers the consumer an excellent alternative to the traditional "Ten-Speed Derailleur" in having a fully automatic torque converter transmission with a new combination "V" and internally toothed belt, both variable and positive drive, combined with an infinitely variable automatic shift mechanism. Instead of having to manipulate multiple levers to obtain the proper speed ratio, one simply pedals the bicycle at a preferred rate of effort with the fully automatic transmission adjusting its speed ratio instantaneously to match grade variations. This is continuously accomplished without it being necessary to momentarily reduce effort in order to "shift", as is necessary with manual transmissions. The torque to time curve with my new transmission is smooth with degree of effort required by the bicycle user being smooth and easy with the effort level determined solely by him whereas it is necessary to momentarily reduce effort in order to "shift", as is necessary with multi-speed transmissions requiring manual shift. Enhanced bicycle safety is also an important consideration in that the new transmission in being fully automatic and continually self adjusting does not divert the rider's attention from traffic in order to shift complicated levers. A bicycle equipped with the new transmission is an excellent exerciser for controlled programs where momentary bursts of physical effort and/or strain are to be avoided.
It is therefore, a principal object of this invention to provide a fully automatic torque converter transmission having low speed positive drive combined with infinitely variable automatic smooth transition shift thereabove for bicycles.
Another object is to provide with such a bicycle transmission elimination of having to manipulate multiple levers to multiple positions to obtain proper speed drive ratios.
A further object is to provide such a bicycle transmission with one simply pedalling a bicycle at a preferred rate of effort with the fully automatic transmission adjusting its speed ratio instantaneously to match grade variations.
Still another object with such a bicycle transmission is greatly enhanced safety with the new transmission being fully automatic and continually self adjusting not diverting the rider's attention from traffic in order to shift complicated levers.
Another object is to provide an excellent bicycle exerciser for controlled health exercise programs where momentary bursts of physical effort and/or strain are to be avoided.
Features of the invention useful in accomplishing the above objects include, in a positive drive to variable speed bicycle automatic torque converter transmission, a fully automatic torque converter transmission using a "V" belt with inner teeth that engage mating teeth on a variable pitch pulley core in a low speed high torque state transformable into an infinitely variable higher speed shift mechanism. The bicycle pedal sprocket drives a pivoted cluster of three small sprockets with a drive chain loop interconnect driving a first sprocket as a driven member, and the other two serving as idlers in maintaining the chain at constant length. A speed ratio of approximately 1:6 from the pedal sprocket to the driven sprocket optimizes torque transmission capacity of the system with the driven sprocket attached to a self-centering, spring loaded, variable pitch pulley. This pulley has a core shaped like a timing belt pulley with grooves (or teeth) at its surface. The "V" belt driven by the variable pitch pulley drives a timing belt type pulley that rotates on a center fixed relative to the bicycle frame, and is a "V" belt with teeth on its inner surface enabling engagement with the variable pitch pulley core at the low speed high torque position. This converts the friction "V" belt drive to a positive drive in low gear. The driven pulley, finally, drives the rear wheel through a conventional bicycle chain. When torque applied to the bicycle pedal sprocket increases, the sprocket cluster tries to rotate about its axis with the tangential force appled by the chain thereby increasing the center distance between the variable pitch pulley and the fixed pulley. The "V" belt expands the variable pitch pulley to correspondingly change the ratio of the power transmission with a power drive transmission having all the characteristics of an infinitely variable torque converter. When torque increases, the transmission "shifts down", when torque is reduced, the transmission automatically "shifts back up" with the geometry of the transmission readily adaptable to a conventional bicycle frame. It can provide a shift range equivalent to a ten-speed "Deraillour" transmission without the need for shift levers, cables, etc. Operation is totally automatic and does not require the bike rider's attention, an important safety feature in bicycle operation. Using different springs in the variable pitch pulley enables the unit to be "customized" to suit different bike riders preference.
A specific embodiment representing what is presently the best mode of carrying out the invention is illustrated in the accompanying drawings.